1. Field of the Invention
This invention relates to an illumination lamp such as a head lamp, a fog lamp or the like and, more specifically, to a lamp called "projector type lamp" which mainly comprises a reflector having two focal points, such as a rotary ellipsoid or a composite ellipsoid, a projection lens for projecting an image of a light source, which is positioned at a first focal point of the reflector, at a second focal point of the reflector, and a shade for controlling light distribution characteristics.
2. Background Art
FIG. 11 shows the configuration of a head lamp as an example of a projector type lamp 90 of the prior art. This projector type lamp 90 comprises a reflector 91 which is formed, for example, as a composite ellipsoid having first and second focal points, a light source 92 positioned at the first focal point, a shade 93 arranged in the vicinity of the second focal point, a projection lens 94 which is an aspherical convex lens having a focal point in the vicinity of the shade 93, and a housing, not shown, for holding these elements at predetermined locations.
Since the head lamp is configured as described above, rays of light from the light source 92 reflected by the reflector 91 are all converged into a light flux at the second focal point. At this point, since the shade 93 is arranged in the vicinity of the second focal point, substantially a lower half portion of the light flux is shaded and an upper half portion is inverted by the projection lens 94, enlarged and projected in an illumination direction to obtain light distribution characteristics for low beams which do not include upward rays.
However, in the above projector type lamp 90 of the prior art, since the projection lens 94 serves as a light emission surface at the time of lighting, the light emission area is smaller than those of lamps of other types which use a parabolic reflector and a cut lens, thereby deteriorating the visibility of the projector type lamp from a car running in an opposite direction or a passenger.
The projection lens 94 appears circular when seen from the front and only the projection lens 94 can be seen when it is installed on a vehicle. Therefore, any lamp provides the same impression. It is substantially impossible to produce a design difference according to the type of a vehicle, even if it is desired. Thus, the projector type lamp of the prior art has such a defect as lack of design freedom.
Further, since the projection lens 94 is smaller than those of the lamps of other types as described above, the heat of the light source 92 is concentrated on the projection lens 94, whereby the temperature of the projection lens 94 rises sharply. Therefore, a glass member must be used to provide heat resistance to the projection lens 94, thereby boosting costs and making it difficult to reduce the weight of the lamp. Solutions to these problems have been awaited.
As for design freedom described above, there has been proposed a method for forming a substantially oval projection lens by cutting end portions in a vertical direction of the projection lens 94 as shown in FIG. 12. In this case, the light emission area becomes much smaller at the time of lighting with the result of deteriorated visibility, a loss in the amount of light and the difficulty of arranging the shade 93. Thus, the formation of light distribution characteristics is restricted and the problems of the prior art cannot be solved.